MINNEAPOLIS - The current battle against the Islamic State in Iraq and Syria (ISIS) has shown that it is anything but a conventional war against terrorists.
First, much of the battle is being waged online - for the hearts and minds of Muslims around the world.
Now, a new phenomenon - that of foreign women signing up as jihadis - has been revealed.
It is being investigated by United States law enforcement officials, who are looking at how women from the American heartland have joined ISIS.
At least three Somali families in the Minneapolis-St Paul area have female relatives who have gone missing in the past six weeks and may have tried to join ISIS, said community leader Abdirizak Bihi.
In a separate case, a 19-year-old American Somali woman from St Paul flew to Turkey last month and joined ISIS in Syria.
Another US teenager, nurse's aide Shannon Conley, 19, from Colorado, pleaded guilty this week to trying to travel to the Middle East to enrol in ISIS. She had been recruited online by a male militant in Syria.
These American women join scores of European Muslim women, mostly from Britain and France, who have joined ISIS in the Middle East.
Sources close to the police worry that the reports of female would-be jihadis could mark a new trend.
"The nature of the recruitment of these crazy organisations is how they use the element of surprise. Now they have surprised us again by going for the girls," said Mr Bihi.
But while foreign women who join ISIS often envision aiding a holy war or at least playing an active role in establishing a purist Islamic nation, the reality can be more mundane.
Monitoring of extremists' social media accounts and other writings shows that male jihadis regard women counterparts as little more than mating partners, said Mia Bloom, from the Centre for Terrorism and Security Studies at the University of Massachusetts Lowell.
"ISIS is recruiting these women in order to be baby factories. They are seeing the establishment of an Islamic state and now they need to populate the state," Professor Bloom said.
"The girls go around making cookies. It's almost like a jihadi Tupperware party," she added.
But the worry for law enforcement agencies is that American militants will one day return to the US and attack targets. "The obvious fear is of individuals coming back and committing a terrorist act here," said Greg Boosalis, the FBI division counsel in Minneapolis.